[TowerTalk] Re: Cable loss differences

[Stan]

Clschmalz wrote:

> Okay -- Here's a question for all you old ET's -- I was checking out
> cables
> yesterday, getting ready for the June contest. I have three home made
> RG-213
> cables (not from the same spool but the same manufacturer) that are
> about the
> same length and fitted with the same  multi-part N connectors. One has
> less
> than 3 dB/100' attenuation at 223.5 MHz (about theoretical for
> RG-213). The
> other two have 4.5 and 5.6 dB/100'.  I'm going to strip and reinstall
> the
> connectors on the latter two cables (I have to anyway on one, I can
> feel the
> center pins). Before I do it however, I'd like to know what are the
> common
> faults in connector fitting that can cause such differences?  Cold
> soldered
> joints? Deformed dielectric? Flux contamination on the end of the
> dielectric?
> ...
>
> Thanks -- Charlie N7SFT



I suspect the difference in cable losses are due to cable degradations
over their length verses the connectors. If the N connector is tight on
the cable and does not spin around, and you can barely feel the male pin
with the tip of your finger, the connector is OK....

coaxial cable losses can be grouped in two:

insertion losses due to dissipation or dissipation losses,

VSWR losses due to non-optimal VSWR ie not 1.0 : 1.0.

dissipation losses are a function of the dielectric material and
the ohmic losses of both the center conductor and the shield.

for a new coaxial cable these losses (per unit length) would be
consistent from
cable to cable from manufacturers production lot to lot.

As the cable gets applied the losses will only get worse over time.

For the best condition of properly applied connectors, use well within
its power ratings,
no exposure to harmful compounds like acids (acid rain) or solvents
(gasoline or petroleum products)
no sharp bends and no flexing.... the degradation over time will be a
minimum or hardly perceivable...

However, when exposed to the outside environment degradation will occur.

If acid rain enters into the coaxial cable either through unsealed ends
or anywhere along its length through pin-hole leaks in the outer sheath
(common manufacturers quality issue), the shield will corrode
resulting in greater ohmic losses....

If the cable is installed vertically,  rain leaking in will hose down
the cable to the lowest point, corroding the outer shield along the way.

Manufacturers may add a "flooding sealant" to prevent hosing.


I hope this helps...


Stan, WA1ECF   Cape Cod, MA   FN41sr






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